Since the early 1970's, bulk tobacco curing has gained wide acceptance in the flue cured tobacco producing regions of the United States. While there may be several factors contributing to its acceptance, probably the single most significant factor was that bulk curing generally required less manual labor than the preceding stick barn method. Further bulk curing was compatible with automatic tobacco harvesters that gained commercial acceptance also at about this same time.
While bulk curing is now a reality and will be for some time to come, the basic design of commercially available bulk tobacco curing and drying structures has not changed significantly since the initial design of F. J. Hassler as shown in U.S. Pat. Nos. 3,105,713 and 3,110,326.
Probably the most significant shortcoming of all conventional bulk curing and drying structures of today is that they are not designed to efficiently utilize fuel. To the contrary, it seems that the basic design of many commercially available bulk tobacco curing and drying structures is such that the structures themselves inherently waste fuel. Some attempts have been made to design more fuel efficient systems, but generally they have not been successful and have not met with commercial success. For example, in this regard, one is referred to U.S. Pat. No. 4,114,288 to Joe W. Fowler. The bulk tobacco curing and drying structure disclosed therein includes a design that attempted to utilize a solar collector and also included an approach in providing bulk tobacco curing and drying structure with a heat exchanger. But neither the heat exchanger design nor the solar collector panel was very efficient and consequently this type of design never obtained great success.
Therefore, there is a real need for the basic design in bulk tobacco curing and drying structures to be improved, especially in the area of efficient fuel utilization. This is particularly so because of the very nature of bulk tobacco curing and drying structures. During the bulk tobacco curing and drying process a continuous system of air is circulated through the structure and the air is heated as necessary to maintain a selected temperature level within the structure. As the tobacco material is dried, the circulating system of air reaches a point where its moisture level or content is such that a portion of the air must be exhausted and fresh inlet outside air must be induced within the curing and drying structure. It is within this area that most, if not all, tobacco curing and drying structures are inherently inefficient. This is because there is not adequate control to control the amounts of exhaust and incoming air and also of great importance is that the exhausted air is very warm and all the heat in the exhaust air is lost in conventional bulk tobacco curing processes.
Finally there is a real need for an improved bulk curing system because of the scarcity of fuel and the continuous escalation of fuel prices.